Excuse me for presuming, but that seems to be a 1st world view of ARM SBCs usage. There are plenty of places in the world where this may be the only computer used until traveling aboard or higher education, so the ability to run actual 'desktop' applications, super cheap, plugged into peripherals, is still a worthy usage of a pi and its ilk.

I have never seen anyone in my third world home country just carrying or even owning an SBC. Even the poorest people just buy a phone because it's wildly more useful and does not require a peripheral. Otherwise, they buy an older computer that can be had for cheaper than most SBCs.

Actually, I'd argue that the market segment is squarely a first world one, mainly because it's far from the most convenient computing platform and alternatives are far more useful when you can only afford to own a single computer. Being unable to make calls or use messaging apps (access to whatsapp is almost a requirement in tons of countries), and coming with no built-in battery makes them a complete non-starter as a potential main device.

To what extent are these used for this use case vs. very inexpensive laptop computers or Chromebooks? In most of my travels I've seen a lot more extremely cheap laptops than ARM SBCs.

I agree that there's a stronger justification for the desktop (and TV-dongle / emulation station, for which there's just a lack of better-suited competition) use case than the home lab one.

Additionally, many places have flaky or nonexistent power infrastructure. Having a computer that runs at 2-3W is a lot easier on small solar + battery than a computer running at 8-10W idle.